Metal plating bath and method of plating



Patented Apr. M, 39421 aerated METAL PLATING BATH AND METHOD OF PLATING John J. Murray, Arlington, Mass.

. No Drawing. Application March 9, 1938,

Serial No. 194,967

8 Claims. "(01. 204-51) This invention relates to a metal plating bath and particularly to a method of plating chroonly with narrow ranges of S04 ion concentration and are very low in efilciency.

In accordance with the present invention a plating solution of relatively high plating elflciency, of considerable stability and one not requiring regulation, is produced.

In accordance with this invention,a halogen derivative of acetic acid, preferably monochloracetic acid, is employed in combination with chromic acid.

The relative concentrations of chromic acid and monochloracetic acid may be widely varied. Preferably, 5% of monochloracetic acid is used based on the chromic acid because at this ratio makeup chromic acid may be added from time to time in the same relative proportion to monochloracetic acid. However, much higher concentrations may be employed as, for example, 9 oz. of monochloracetic acid to 36 oz. of chromic acid, or as little as 1% may be employed. At the higher concentrations the plating is heavier and the solution tends to heat more rapidly. At the lower concentrations the plating is not so heavy.

A preferred plating bath comprises. to each gallon of water 36 oz. of chromic acid and 2 oz.

of monochloracetic acid. With such a bath, it is preferable to use a lead electrode.

7 The solution may be run hot or cold, but is preferably run from 90 to 130 F. The current density may be widely varied.

and produces a copper film which has considerof chromic acid to 2- oz. of monochloracetic acid,

the deposit on a square foot. is approximately .0003" in five minutes. This uses up approximately V oz. oi chromic acid and a correspondin: amount or monochloracetic acid. Accordingly, make-up is added periodically in the origi- 4 nal ratio of 38 to 2 and the process may be operated for months without any analysis, by-making it up in this manner.

For the brighter chromium finishes, it is preferred to keep the current density lower,.ior example, plating only .00015 in four minutes.

In the bathherein described. chromium plating Y the bath without any previous cleaning whatsoever, if desired.

The dichloracetic acid and trichloracetic acid, while operating satisfactorily, are more expensive and are more corrosive to the hands. These are likewise used around 5%.

Metallic chromium produced in the layers by this process has a considerablydifierent appearance than the ordinary electrolytic chromium. It has a more metallic look, is heavy, less brittle, and is not-full of cracks.

The solution'may likewise be used to plate lead, employing a lead nitrate bath. For example, in one gallon of water saturated with leadnitrate 10% of glycerin and 5% of monochloracetic acid are employed based on the lead. a low current density is employed and the bath is preferably cold. The use of monochloracetic acid likewise increases the efiiciency of a copper plating bath able strength and the color oi which resembles that of copper produced by cooling from fusion.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, but the appended claims should be construed as broadly as permissible in view of the prior art.

I claim: 1. A chromium plating bath comprising chro- -mic acid and a minor proportion of a chlorinated 4. A plating bath comprising water, chromic. acid and monochloracetic acid, the monochloracetic'belng 1 to 25% of the chromicgacid by weight.

5. A process for electroplating chromium,-

which comprises passing an eiectriccurrent from an anode to a cathode through an aqueous solution of chromic acid and monochloracetic acid.

6. The method as set forth in claim 5, in which the bath comprises approximately 1 gallon of water, 36 ounces of chromic acid and 2 to 9 ouncesof monochloracetic acid.

7. The method as set forth in claim 5, in which the bath comprises water, chromic acid and monochloracetic acid in the proportion oil to 25% or chromic acid by weight. V p 8. The method of plating chromium which.v

comprises passing an electric current through an electrolyte solution comprisingchromic acid and a minor proportion of a chlorinated acetic acid.

' JQHN J'.'MURRAY. 

